Normally closed (dry contact) switch operation is a requirement for some nurse call devices. Previous nurse call devices used tact or pushbutton switches, and therefore providing a normally closed switch that opens upon actuation has not been problematic.
However, newer generation nurse call devices use metallic dome switches. A nurse call device using dome switches is described in commonly-owned U.S. patent application Ser. No. 12/362,501, now U.S. Patent Application Publication No. 2010/0195295 A1, the disclosure of which is incorporated herein by reference. Metallic dome switches of the prior art are designed as normally open switches, such that the switch is closed upon actuation. In normally open dome switches of the prior art, a printed circuit board includes a switch trace having a ring-shaped first contact area and a central second contact area located within the ring of the first contact area and spaced from the first contact area so as to be electrically insulated from the first contact area, and a metallic dome is arranged to have its support legs in contact with the first contact area and its central portion spaced above the second contact portion. In this arrangement, the switch can be closed by pressing the central portion of the metallic dome sufficiently to cause the central portion to contact the second contact area of the switch trace on the printed circuit board. When pressure on the dome is released, the dome resiliently returns to its original position and the switch is re-opened.
What is needed is a normally closed dome switch that opens when the dome is pressed.